Fairly uniform poly(styrene)-poly(methyl methacrylate) (PST-PMMA) composite microspheres were prepared by employing an SPG (Shirasu Porous Glass) membrane emulsification technique. A mixture of PST, PMR;LA, and cosurfactant [lauryl alcohol (LOH)] dissolved in dichloromethane (DCM) was used as the dispersed phase, and an aqueous phase containing poly(vinyl alcohol) and sodium lauryl sulfate was used as the continuous phase. It is necessary to add LOH to obtain uniform particles with the SPG emulsification technique. The effects of the volume of LOH on the morphology of the final particles were investigated by varying the volume of LOH from 0 to 2 ml (per 1.2 g polymer). A three-component model was developed for different PR PMMA/PST ratios and LOH/polymer ratios, based on Sundberg's theory; and the calculation on morphology was carried out by using the three-component model. Agreement was obtained between experimental and calculated results. When 2 ml of LOH was added, it was found that LOH can engulf the polymer particles completely; a hemicore (HCP1P2P3) morphology, where PST and PMMA formed a hemisphere core inside a LOH shell, was observed when the PMMA/PST ratio was high, while core-shell-shell (CSP1P2P3) morphology, where PMMA formed a core and PST and LOH formed an inner shell and an outer shell, respectively, was observed when the PMMA/PST ratio was low. When the volume of LOH was below 1 ml (per 1.2 g polymer), however, LOH could not always engulf the inner polymer particles completely; cored hemisphere (CHSP3P2P1), core-shell-shell (CSP2P1P3), and hemicore (HCP1P2P3) morphologies were observed, depending on the PMMA/PST ratio and volume of LOH.